Alcohols, and in particular methanol and ethanol, are fuel substitutes which when added in low percentages to the hydrocarbons offer the advantage of providing a fuel mixture requiring no modification nor any specific adjustment of the conventional gasoline engines. However it has been observed that these mixtures are very sensitive to traces of water which cause the segregation of the mixture, such that the liquid is separated into two phases of different densities: an upper phase contains most of the hydrocarbons and a lower, polar phase rich in alcohol. This segregation phenomenon is more pronounced at lower temperatures of the mixture. The concentration of water in the mixture which causes the segregation is termed the "segregation threshold," and is related to the temperature of the mixture. In practice it is nearly impossible to rigorously prevent water presence in this type of mixture because of the mixture's inevitable contact with humid atmospheres during storage, shipping and marketing. Illustratively a content of 500 ppm of water suffices to segregate a mixture at 11.degree. C. of 5% methanol and 95% premium fuel.
U.S. Pat. No. 4,279,620 describes a process for stabilizing a mixture of premium fuel and ethanol, wherein the mixture is dried by being placed in contact with a saturated CaCl.sub.2 solution and with solid CaCl.sub.2. It is a fairly tricky matter to implement this process in two stages and moreover, as the calcium chloride becomes deliquescent after hydration, it becomes the source of serious difficulties where the process takes place in industry and continuously with a fixed bed.
In industry, the presently used water-adsorbents used in a fixed bed are mainly alumina, molecular sieves and silica gel. However the regeneration of the former two adsorbents takes place at high temperatures (250.degree. to 300.degree. C.) and leads to substantial power consumption, which if, resorted to, would unfavorably affect the overall energy efficiency of the alcohol fuels. While silica gel can be regenerated at lower temperatures, it is on the other hand mechanically fragile and thereby requires care when being used.
Furthermore the inventors have noted in the lab that the water adsorption kinetics of these adsorbents is low in the alcohol/hydrocarbon medium and therefore the application of these adsorbents presents difficulties in industry and in the fixed-bed method.
An object of the present invention is to provide a novel treatment method for alcohol-containing fuels in order to prevent segregation of the fuel mixture and to stabilize their homogeneity.
One of the main objectives of the invention is to provide a method which is economical of energy.
Another object is to ensure rapid treatment so as to make possible treating large amounts of fuels with moderate amounts of adsorbents.
Another object is to enable continuous industrial implementation of fuel conditioning.
Still another object of the invention is to provide a novel adsorbent offering preferential affinity for water and permitting drying in the presence of polar compounds.